Liquid diffuser devices as used in irrigation systems for delivery of water or other liquids, commonly known as “sprinklers”, comprise a support frame which is designed to be connected to the hydraulic system and has a nozzle for directing the liquid jet to a specially shaped diffusion plate.
The latter is in turn mounted to a deflecting member, having a rotating stem of such a size as to move, under jet pressure, with a combined motion of rotation about its own central axis and rotation or precession about the jet-defined axis, for uniform peripheral deflection of the jet.
In certain prior art solutions, as described for instance in U.S. Pat. No. 5,950,927 and U.S. Pat. No. 6,176,440, the stem has a lower portion formed with a conical or spheroidal rolling surface, which is designed to roll on a rolling track, also of conical or spheroidal shape, formed in the lower part of the frame.
These solutions have the apparent drawback of not allowing constant coupling of the surface and the rolling track, which results in a high risk of the jet being unevenly deflected.
Furthermore, the normal operating pressures exerted by the jet on the deflector body cause deformations of the two contact surfaces, resulting in an efficiency loss.
U.S. Pat. No. 5,439,174 discloses a device in which the stem and the frame are coupled by a CV joint which locks the stem, and hence the hole deflector body, in the axial direction, while allowing it to rotate and oscillate.
The joint is composed of a spherical element integral with the lower end of the stem and housed in a concavity formed in the lower part of the frame, within which the spherical element can rotate.
However, also in this case, normal operating pressures may cause deformation of the spherical element and, as a result, a downward shift, even though to a little extent, of the deflector body.
Thus, the distance of the plate from the nozzle will be longer than the optimal device calibration distance, and the jet will not be optimally deflected.
U.S. Pat. No. 5,588,595 discloses another deflector device similar to the one described above, in which the spherical element is locked in a roller cage containing a plurality of coplanar spaced ball bearings.
The spherical element is placed at the center and simultaneously contacts all the rollers to allow stem oscillations.
However, also in this case, the deformations of the various spherical components, caused by jet pressure, may cause a change of the initial orientation of the device, resulting in an inefficient operation thereof.
Furthermore, the roller cage is greatly susceptible to the building up of foreign matter, i.e. dust and sand, with a high risk of irregular operation, which might also lead to total blockage.